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Frequency Generation; Synthesizer: The Discrete Vcxo (26mhz) - Siemens C45 Repair Documentation

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4.2 Frequency generation

4.2.1 Synthesizer: The discrete VCXO (26MHz)

M46 mobile is using a reference frequency of 26MHz for the Hitachi chip set.
The generation of the 26MHz signal is done via a discrete "Colpitts" VCXO .
This oscillator consists mainly of:
A 26MHz crystal
An oscillator switch
A capacity diode
TP 951 after dividing by two
The oscillator output signal is directly connected to the BRIGHT IC (pin 38) to be
used as reference frequency inside the Bright and to be divided by 2.
This so gained signal
SIN13MHZ_BB
To compensate frequency drifts (e.g. caused by temperature) the oscillator
frequency is controlled by the (AFC_PNM) signal, generated through the internal
EGOLD+
(D100
(functional R3)
Reference is the base station frequency.
To compensate a temperature caused frequency drift, the temperature-depending
resistor
R959
is placed near the VCXO to measure the temperature. The
measurement result
TVCXO
the signal TENV.
The required voltage
VCC_OSC
R863
and
R861
Waveform of the AFC_PNM signal from EGOLD+ to Oscillator
S ig n a lfo rm
E G O L D +
V 1 .3
1
R 1 0 6
A F C
3 0 K
V1.0
C45, M50 AND MT50
Z950
V950
V951
is used from the EGOLD+
) PLL via the capacity diode V951.
is reported to the EGOLD+
is provided by the
1
2
V 6 0 2
B A S 1 7 0 W
2
R 6 1 5
A F C _ P N M
4 7 K
G N D
Page 9 of 46
Company Confidential © Copyright Siemens AG
(functional M14)
via
(baseband L4)
N840 (VCC_SYN)
through
3
3
R 6 0 0
2 2 K
G N D
G N D
.
R136
as
ICM MP CCQ ST
05/02

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